This invention relates to compression release engine brakes, and more particularly to a compact mechanism for performing lash adjusting and slave piston reset functions in such brakes.
Compression release engine brakes are well known as shown, for example, by such references as Laas U.S. Pat. No. 3,405,699, Custer U.S. Pat. No. 4,398,510, Cavanagh U.S. Pat. No. 4,399,787, Hu U.S. Pat. No. 5,161,501, and Custer U.S. Pat. No. 5,186,141, all of which are hereby incorporated by reference herein. The two Custer patents mentioned above relate to mechanisms for automatically adjusting the "lash" of an engine brake when the brake is turned on or off. The lash is the cold-engine clearance between each slave piston in the engine brake and the engine component on which that slave piston acts when the engine brake is turned on. It is typically desirable to have this clearance be relatively large when the engine brake is off to ensure that the engine brake does not inadvertently hold open the exhaust valves of the engine, especially when the engine is hot and thermally expanded. On the other hand, it is typically desired to reduce this clearance when the engine brake is on so that optimal timing of exhaust valve openings produced by the engine brake is achieved. For this purpose the Custer patents show mechanisms for automatically moving the return stop of the slave piston when the engine brake is turned on. In general, these lash-adjusting mechanisms include a chamber which tends to enlarge (through the action of a spring) when the slave piston reciprocates away from the return stop. The chamber fills with hydraulic fluid, which is then substantially prevented from escaping (e.g., by the returned slave piston). The trapped fluid maintains the chamber in its enlarged size as long as the engine brake is on, thereby providing a new return stop position for the slave piston. When the engine brake is turned off, the hydraulic fluid gradually leaks out of this chamber, thereby allowing the slave piston to return to its original return stop position.
While the engine brake is on, the slave piston is typically reciprocated by hydraulic fluid flow from a master piston in the engine brake. The master piston derives its motion from a moving part of the engine such as a fuel injector push rod. Although the forward stroke of this engine part may have suitable characteristics for the desired slave piston forward stroke, the return stroke of this engine part often does not result in an acceptable return stroke of the slave piston. For example, the return stroke of the engine part may be so gradual and prolonged that the slave piston continues to hold open the associated exhaust valves through the normal exhaust stroke opening of those valves. Among the possible disadvantages of this are (1) sharp discontinuities in exhaust valve motion when the normal exhaust valve opening occurs, and (2) the risk of contact between the still-open exhaust valves and the associated engine piston near top dead center of the exhaust stroke.
To prevent the engine brake from opening the exhaust valves longer than necessary to produce the desired compression release events, the above-mentioned Cavanagh patent shows mechanisms for resetting the slave piston promptly after each compression release event and even though the associated master piston does not reset until substantially later. Such slave piston reset mechanisms typically operate by snapping open an aperture in the slave piston when the occurrence of a compression release event in the associated engine cylinder allows the pressure in the slave piston cylinder to drop below a certain value. Opening the slave piston aperture allows hydraulic fluid to escape from the slave piston cylinder, thereby allowing the slave piston return springs and other associated components to produce a return stroke of the slave piston, even though the master piston return stroke will not occur until later.
It is also known to "clip" the forward stroke of the slave piston (e.g., to prevent excessive travel of the associated engine exhaust valves which could cause them to contact the top of the engine piston at or near its top dead center position). Mechanisms for producing such slave piston clipping are shown, for example, in Laas U.S. Pat. No. 3,405,699 and Hu U.S. Pat. No. 5,161,501. These mechanisms typically include components for opening an aperture in the slave piston when the forward stroke of the slave piston has progressed to a predetermined point. This allows hydraulic fluid to bleed from the slave piston cylinder, thereby preventing the slave piston from moving forward beyond the point at which the aperture is opened. A typical clip valve mechanism does not have the snap-open action of a slave piston reset mechanism as in the above-mentioned Cavanagh patent. A clip valve mechanism therefore does not actually reset the slave piston like a reset mechanism does.
Both the automatic lash adjusting function (as in the Custer patents) and the slave piston resetting function (as in the Cavanagh patent) are sometimes needed. Devices which combine these functions are known as shown by Meistrick et al. U.S. Pat. No. 4,706,625, but it has been difficult to combine these functions in a compact, simple, and low cost way.
In view of the foregoing, it is an object of this invention to improve and simplify the provision of combined automatic lash adjusting and slave piston resetting mechanisms for compression release engine brakes.
It is another object of this invention to provide a relatively simple and compact mechanism which combines the functions of automatic lash adjustment and slave piston resetting for compression release engine brakes.